The present invention relates generally to improvements in fluid driven hydraulic pumps and more particularly to improvements in fluid driven motors used in such hydraulic pumps to drive the hydraulic pumps.
Fluid actuated hydraulic fluid pressure producing units are shown, for example, in U.S. Pat. No. 3,041,975, issued July 3, 1962 to Atherton et al. in U.S. Pat. No. 3,463,053, issued Aug. 26, 1969 to Leibundgut, both of these patents assigned to an assignee in common with that of the present invention. Another type of similar device is shown in U.S. Pat. No. 3,788,781, issued Jan. 29, 1974 to McClocklin.
Fluid actuated hydraulic power units of the type referred to in the above patents are generally intended to use a source of fluid pressure, such as air pressure commonly used in garages, salvage operations, or in industrial applications, and at pressures on the order of 100 psi, to supply high pressure hydraulic fluid at pressures on the order of 10,000 psi to operate hydraulic fluid motors or other hydraulic tools. Such hydraulic power units include a reciprocating piston air motor, the piston being driven by air pressure and functional to reciprocate a piston of a hydraulic pump to thereby drive the hydraulic pump and supply high pressure hydraulic fluid through an output passage to a hydraulic tool or the like.
A disadvantage of the prior art fluid actuated hydraulic power units is that the air motors used therein operate in such a manner that air flows through the air motor continuously during both the input stroke and the exhaust stroke of the air motor piston. During the exhaust stroke of the air motor, air flow into the air motor is unnecessary, and the input air must be diverted directly through the motor to the motor exhaust port and thus to the ambient atmosphere. As a result of the continuous flow of compressed air through the air motor, the prior art apparatus is relatively ineffecient in that it employs unnecessary amounts of compressed air and it has the further disadvantage that the large volume of air flowing through the air motor creates an undesirable and unnecessary noise level. The noise generated by the air motor is particularly noticeable during the exhaust stroke of the air motor when the compressed air in the air motor chamber is forced through an exhaust passage and at the same time the air being supplied to the air motor is also being exhausted through this air passage. The resulting high volume of air flowing through this exhaust passage at a high velocity creates a substantial noise level.